Molecular weight of specific biopolymers is an important parameter in characterizing the molecule, its position and orientation in situ and its interactions with other compounds. Measurements of molecular weight are accomplished by several different techniques which depend on chemical or physical properties of these structures, and all of which demand purified samples. An alternative method is that of radiation inactivation. By means of target analysis it is possible to evaluate a molecular weight which depends on different properties, the functional activities of the specific biopolymer. It is an important feature of this technique that crude samples can be used. The physical basis for this approach has been described long ago, but as the method is applied to more complicated systems and more complex structures, new questions arise. These involve interactions between subunits of proteins, effects of a lipid environment as in membranes, or the presence of carbohydrates. Experimental procedures which modify the natural order of things -- treatment with detergents, for example -- could also change the radiation-sensitive unit detected by enzymatic activity or receptor function. Analysis of these effects is an important phase of this project on molecular weight determination by radiation inactivation.